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SubjectRe: Usefulness of CONFIG_MACH_JZ47*


Le mar., sept. 20 2022 at 16:19:41 +0200, H. Nikolaus Schaller
<hns@goldelico.com> a écrit :
> Hi Paul,
>
>> Am 20.09.2022 um 15:33 schrieb Paul Cercueil <paul@crapouillou.net>:
>>
>>
>>
>> Le mar., sept. 20 2022 at 14:31:38 +0200, H. Nikolaus Schaller
>> <hns@goldelico.com> a écrit :
>>> Hi Paul,
>>>> Am 20.09.2022 um 11:09 schrieb Paul Cercueil
>>>> <paul@crapouillou.net>:
>>>> Hi Nikolaus,
>>>> Le mar., sept. 20 2022 at 08:31:30 +0200, H. Nikolaus Schaller
>>>> <hns@goldelico.com> a écrit :
>>>>> Hi Paul,
>>>>> it seems as if there aren't many places left over where the
>>>>> MACH_JZ47* configs are still in use:
>>>>> drivers/char/hw_ramdom/Kconfig
>>>>> drivers/clk/ingenic/Kconfig
>>>>> drivers/gpu/drm/ingenic/Kconfig
>>>>> drivers/pinctrl/pinctrl-ingenic.c
>>>>> Is it possible to get rid of them and just have
>>>>> CONFIG_MACH_INGENIC_GENERIC?
>>>>> This might simplify my defconfig for multiple machines.
>>>> CONFIG_MIPS_GENERIC_KERNEL=y
>>> This breaks compilation for me, e.g.
>>> arch/mips/mm/cache.c:203:6: error: 'cpu_has_tx39_cache' undeclared
>>> (first use in this function)
>>
>> v6.0-rc does not have 'cpu_has_tx39_cache' anywhere in that file,
>> or in arch/mips/ for that matter. It was removed in v5.18.
>>
>> And a v5.17 kernel compiles fine here with these options enabled.
>> So it's a problem on your side, I guess.
>
> Ah, you were right.
>
> I have a patch included which was provided by
> zhouyanjie@wanyeetech.com
> ("MIPS: mm: Add Ingenic XBurst SoCs specific cache driver.").
>
> It is intended to improve caching and is part of jz4780 SMP support
> which we wanted to have.
> AFAIR it was either not posted to lkml or rejected or superseded.
>
>>
>>>> CONFIG_BOARD_INGENIC=y
>>> This config option does not exist (at least in v6.0-rc). Probably
>>> you refer to CONFIG_INGENIC_GENERIC_BOARD.
>>
>> No, I do not, and yes, it exists.
>
> Ah, I grepped for CONFIG_BOARD_INGENIC but it exists only in one
> Kconfig as BOARD_INGENIC.
> But what is then the difference to CONFIG_INGENIC_GENERIC_BOARD and
> CONFIG_MACH_INGENIC_GENERIC?

CONFIG_BOARD_INGENIC=y means you are building a generic MIPS kernel
that happens to support Ingenic boards. In this case, the kernel has a
lot of features enabled that might not be useful on specific Ingenic
boards, because the kernel needs to support other SoCs. This option
selects CONFIG_MACH_INGENIC_GENERIC=y, which in turn selects
MACH_INGENIC=y and every MACH_JZ* and MACH_X* there is.

If you instead set MACH_INGENIC_SOC=y as your "Machine Selection ->
System Type", this means your kernel will run specifically on Ingenic
SoCs and isn't expected to work anywhere else. By default the "Machine
Type" will be CONFIG_INGENIC_GENERIC_BOARD=y aka. "Generic board",
which can be used to support any board with an Ingenic SoC. This option
also selects CONFIG_MACH_INGENIC_GENERIC=y. If you choose a different
"machine type", for instance JZ4780_CI20=y, then only MACH_JZ4780=y
will be selected, and all the code unrelated to the JZ4780 SoC will be
disabled.

Cheers,
-Paul

>
>>
>>> As far as I see, this does not choose to build any device tree
>>> blob.
>>> I tried some patch to get the .dtb built, but the resulting kernel
>>> does not show any activity.
>>> If I e.g. switch back from CONFIG_INGENIC_GENERIC_BOARD=y to
>>> CONFIG_JZ4780_CI20=y the kernel works.
>>
>> Because in the first case you build a generic kernel, which does
>> not embed any .dtb, and you are responsible for providing the kernel
>> with the blob at boot time; while if you build with
>> CONFIG_JZ4780_CI20=y it embeds the .dtb inside the kernel.
>>
>> You can embed the .dtb into the generic kernel at compile-time too,
>> have a look at "Kernel type -> Kernel appended dtb support." Not
>> sure why you'd want that for a generic kernel, though.
>
> Ah, I remember. Since I usually code 99% of my time for ARM systems
> with separate .dtb files chosen by the boot loader, I forgot that we
> have to append the .dtb on the CI20 and Alpha400. So there is no good
> solution for a "universal" kernel binary either.
>
>>
>>>> Then you can support all Ingenic-based boards alongside other
>>>> MIPS boards.
>>> Yes, I know, but why are the MACH_JZ47* not replaced by
>>> CONFIG_MACH_INGENIC_GENERIC if they are almost unused or completely
>>> removed?
>>
>> They *are* used.
>
> Well, only in a handful of places as it looks like.
>
>>
>>> BTW: there are also seems to be some board specific CONFIGs in
>>> processor specific code (e.g. CONFIG_JZ4780_CI20 in irqchip code).
>>
>> rgrep CI20 drivers/irqchip/
>>
>> returns nothing for me.
>
> Ah, again an inofficial patch which is part of the SMP stuff
> ("irqchip: Ingenic: Add percpu IRQ support for X2000.").
>
>>
>>> So selecting a MACH is not sufficient to get these features.
>>> All this looks a little fragile and incomplete... Maybe if I find
>>> some time (which is unfortunately quite unlikely) I can propose
>>> some fixes.
>>
>> It is not "fragile and incomplete", it works as intended, and it's
>> a feature I use often.
>
> Yes, seems as if you are right. We may have added too many useful
> patches which did not go upstreamand get in conflict with upstream
> features.
>
> BR and thanks for helping to better understand,
> Nikolaus
>
>>
>> -Paul
>>
>


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